Mobile communication systems were developed to provide mobile users with communication services. With the rapid advance of technologies, the mobile communication systems have evolved to the level capable of providing high speed data communication service beyond the early voice-oriented services.
Recently, standardization for a Long Term Evolution (LTE) system, as one of the next-generation mobile communication systems, is underway in the 3rd Generation Partnership Project (3GPP). LTE is a technology for realizing high-speed packet-based communications with the data rate of up to 100 Mbps, which is higher than the currently available data rate, and its standardization is almost complete.
In line with the completion of the LTE standardization, an LTE-Advanced (LTE-A) system is now under discussion, which improves a transfer rate by combining the LTE communication system with several new technologies. One of such technologies is Carrier Aggregation. The Carrier Aggregation is a technology allowing a terminal to use multiple downlink carriers and multiple uplink carriers unlike the conventional technology of using one downlink carrier and one uplink carrier for data communication.
Assuming that a cell is configured with one downlink carrier and one uplink carrier in the conventional concept, the carrier aggregation can be understood as if the UE communicates data via multiple cells. With the use of carrier aggregation, the peak data rate increases in proportion to the number of aggregated carriers.
In the following description, if a UE receives data through a certain downlink carrier or transmits data through a certain uplink carrier, this means to receive or transmit data through control and data channels provided in cells corresponding to center frequencies and frequency bands characterizing the carriers.
In the present Invention, carrier aggregation may be expressed as configuring a plurality of serving cells. At this time, the plurality serving cells include a primary serving cell (PCell) and secondary serving cell (SCell).
Other terms to describe the embodiments of the present invention are used in the meanings as used in the LTE system and specified in TS36.331 and TS36.321 (December, 2011).
In line with the widespread use of smartphone an always-on type services, the number of terminals in connected state increases and, as a consequence, this increases the probability of congestion on the random access channel. An embodiment of the present invention proposes a method and apparatus for applying congestion control to the terminal in the connected state to solve the above problem.
As aforementioned, the introduction of the carrier aggregation increases the achievable data rate dramatically, it is restrictive to increase the data rate actually doe to the intrinsic problem of layer 2 (e.g. short length of sequence number). An embodiment of the present invention proposes a method and apparatus to extend the layer sequence number.